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Browsing by Subject "Live cell imaging"
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Item Live Imaging of Type I Collagen Assembly Dynamics in Osteoblasts Stably Expressing GFP and mCherry-Tagged Collagen Constructs(Wiley, 2018-06) Lu, Yongbo; Kamel-El Sayed, Suzan A.; Wang, Kun; Tiede-Lewis, LeAnn M.; Grillo, Michael A.; Veno, Patricia A.; Dusevich, Vladimir; Phillips, Charlotte L.; Bonewald, Lynda F.; Dallas, Sarah L.; Anatomy and Cell Biology, IU School of MedicineType I collagen is the most abundant extracellular matrix protein in bone and other connective tissues and plays key roles in normal and pathological bone formation as well as in connective tissue disorders and fibrosis. Although much is known about the collagen biosynthetic pathway and its regulatory steps, the mechanisms by which it is assembled extracellularly are less clear. We have generated GFPtpz and mCherry-tagged collagen fusion constructs for live imaging of type I collagen assembly by replacing the α2(I)-procollagen N-terminal propeptide with GFPtpz or mCherry. These novel imaging probes were stably transfected into MLO-A5 osteoblast-like cells and fibronectin-null mouse embryonic fibroblasts (FN-null-MEFs) and used for imaging type I collagen assembly dynamics and its dependence on fibronectin. Both fusion proteins co-precipitated with α1(I)-collagen and remained intracellular without ascorbate but were assembled into α1(I) collagen-containing extracellular fibrils in the presence of ascorbate. Immunogold-EM confirmed their ultrastuctural localization in banded collagen fibrils. Live cell imaging in stably transfected MLO-A5 cells revealed the highly dynamic nature of collagen assembly and showed that during assembly the fibril networks are continually stretched and contracted due to the underlying cell motion. We also observed that cell-generated forces can physically reshape the collagen fibrils. Using co-cultures of mCherry- and GFPtpz-collagen expressing cells, we show that multiple cells contribute collagen to form collagen fiber bundles. Immuno-EM further showed that individual collagen fibrils can receive contributions of collagen from more than one cell. Live cell imaging in FN-null-MEFs expressing GFPtpz-collagen showed that collagen assembly was both dependent upon and dynamically integrated with fibronectin assembly. These GFP-collagen fusion constructs provide a powerful tool for imaging collagen in living cells and have revealed novel and fundamental insights into the dynamic mechanisms for the extracellular assembly of collagen.Item Monitoring endosomal trafficking of the G protein-coupled receptor somatostatin receptor 3(Elsevier, 2014) Tower-Gilchrist, Cristy; Styers, Melanie L.; Yoder, Bradley K.; Berbari, Nicolas F.; Sztul, Elizabeth; Biology, School of ScienceEndocytic trafficking of G protein-coupled receptors (GPCRs) regulates the number of cell surface receptors available for activation by agonists and serves as one mechanism that controls the intensity and duration of signaling. Deregulation of GPCR-mediated signaling pathways results in a multitude of diseases, and thus extensive efforts have been directed toward understand the pathways and molecular events that regulate endocytic trafficking of these receptors. The general paradigms associated with internalization and recycling, as well as many of the key regulators involved in endosomal trafficking of GPCRs have been identified. This knowledge provides goalposts to facilitate the analysis of endosomal pathways traversed by previously uncharacterized GPCRs. Some of the most informative markers associated with GPCR transit are the Rab members of the Ras-related family of small GTPases. Individual Rabs show high selectivity for distinct endosomal compartments, and thus co-localization of a GPCR with a particular Rab informs on the internalization pathway traversed by the receptor. Progress in our knowledge of endosomal trafficking of GPCRs has been achieved through advances in our ability to tag GPCRs and Rabs with fluorescent proteins and perform live cell imaging of multiple fluorophores, allowing real-time observation of receptor trafficking between subcellular compartments in a cell culture model.